Eccentric abrading and cutting head for high-speed rotational atherectomy devices

ABSTRACT

The invention provides a rotational atherectomy device having, in various embodiments, a flexible, elongated, rotatable drive shaft with at least one flexible or inflexible eccentric enlarged abrading and cutting head attached thereto which comprises an abrasive surface. When placed against stenotic tissue and rotated at high speed, the eccentric nature of the abrading and cutting head moves along an orbital path, opening the lesion to a diameter larger than the resting diameter of the enlarged abrading and cutting head. Preferably the abrading and cutting head has a center of mass spaced radially from the rotational axis of the drive shaft, facilitating the ability of the device to travel along an orbital path. The abrading and cutting head comprises proximal and/or distal radiused surfaces that facilitate cutting difficult stenosis material while minimizing trauma to the vessel. In some cases, the abrading and cutting head is made from a relatively dense metal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.12/130,024, filed on May 30, 2008.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to devices and methods for removing tissue frombody passageways, such as removal of atherosclerotic plaque fromarteries, utilizing a high-speed rotational atherectomy device.

2. Description of the Related Art

A variety of techniques and instruments have been developed for use inthe removal or repair of tissue in arteries and similar bodypassageways. A frequent objective of such techniques and instruments isthe removal of atherosclerotic plaques in a patient's arteries.Atherosclerosis is characterized by the buildup of fatty deposits(atheromas) in the intimal layer (under the endothelium) of a patient'sblood vessels. Very often over time, what initially is deposited asrelatively soft, cholesterol-rich atheromatous material hardens into acalcified atherosclerotic plaque. Such atheromas restrict the flow ofblood, and therefore often are referred to as stenotic lesions orstenoses, the blocking material being referred to as stenotic material.If left untreated, such stenoses can cause angina, hypertension,myocardial infarction, strokes and the like.

Rotational atherectomy procedures have become a common technique forremoving such stenotic material. Such procedures are used mostfrequently to initiate the opening of calcified lesions in coronaryarteries. Most often the rotational atherectomy procedure is not usedalone, but is followed by a balloon angioplasty procedure, which, inturn, is very frequently followed by placement of a stent to assist inmaintaining patency of the opened artery. For non-calcified lesions,balloon angioplasty most often is used alone to open the artery, andstents often are placed to maintain patency of the opened artery.Studies have shown, however, that a significant percentage of patientswho have undergone balloon angioplasty and had a stent placed in anartery experience stent restenosis, which is blockage of the stent thatmost frequently develops over a period of time as a result of excessivegrowth of scar tissue within the stent. In such situations anatherectomy procedure is the preferred procedure to remove the excessivescar tissue from the stent (balloon angioplasty being not very effectivewithin the stent), thereby restoring the patency of the artery.

Several kinds of rotational atherectomy devices have been developed forattempting to remove stenotic material. In one type of device, such asthat shown in U.S. Pat. No. 4,990,134 (Auth), a burr covered with anabrasive abrading material such as diamond particles is carried at thedistal end of a flexible drive shaft. The burr is rotated at high speeds(typically, e.g., in the range of about 150,000-190,000 rpm) while it isadvanced across the stenosis. As the burr is removing stenotic tissue,however, it blocks blood flow. Once the burr has been advanced acrossthe stenosis, the artery will have been opened to a diameter equal to oronly slightly larger than the maximum outer diameter of the burr.Frequently more than one size burr must be utilized to open an artery tothe desired diameter.

U.S. Pat. No. 5,314,438 (Shturman) discloses another atherectomy devicehaving a drive shaft with a section of the drive shaft having anenlarged diameter, at least a segment of this enlarged surface beingcovered with an abrasive material to define an abrasive segment of thedrive shaft. When rotated at high speeds, the abrasive segment iscapable of removing stenotic tissue from an artery. Though thisatherectomy device possesses certain advantages over the Auth device dueto its flexibility, it also is capable only of opening an artery to adiameter about equal to the diameter of the enlarged abrading surface ofthe drive shaft since the device is not eccentric in nature.

U.S. Pat. No. 6,494,890 (Shturman) discloses a known atherectomy devicehaving a drive shaft with an enlarged eccentric section, wherein atleast a segment of this enlarged section is covered with an abrasivematerial. When rotated at high speeds, the abrasive segment is capableof removing stenotic tissue from an artery. The device is capable ofopening an artery to a diameter that is larger than the resting diameterof the enlarged eccentric section due, in part, to the orbitalrotational motion during high speed operation. Since the enlargedeccentric section comprises drive shaft wires that are not boundtogether, the enlarged eccentric section of the drive shaft may flexduring placement within the stenosis or during high speed operation.This flexion allows for a larger diameter opening during high speedoperation, but may also provide less control than desired over thediameter of the artery actually abraded. In addition, some stenotictissue may block the passageway so completely that the Shturman devicecannot be placed therethrough. Since Shturman requires that the enlargedeccentric section of the drive shaft be placed within the stenotictissue to achieve abrasion, it will be less effective in cases where theenlarged eccentric section is prevented from moving into the stenosis.The disclosure of U.S. Pat. No. 6,494,890 is hereby incorporated byreference in its entirety.

U.S. Pat. No. 5,681,336 (Clement) provides a known eccentric tissueremoving burr with a coating of abrasive particles secured to a portionof its outer surface by a suitable binding material. This constructionis limited, however because, as Clement explains at Col. 3, lines 53-55,that the asymmetrical burr is rotated at “lower speeds than are usedwith high speed ablation devices, to compensate for heat or imbalance.”That is, given both the size and mass of the solid burr, it isinfeasible to rotate the burr at the high speeds used during atherectomyprocedures, i.e., 20,000-200,000 rpm. Essentially, the center of massoffset from the rotational axis of the drive shaft would result indevelopment of significant centrifugal force, exerting too much pressureon the wall of the artery and creating too much heat and excessivelylarge particles.

Commonly assigned U.S. patent application Ser. No. 11/761,128 entitledEccentric Abrading Head for High-Speed Rotational Atherectomy Devices,discloses certain embodiments of an eccentric abrading head.Specifically, application Ser. No. 11/761,128 discloses a flexible,elongated, rotatable drive shaft with at least one flexible, ornon-flexible, eccentric enlarged abrading head attached thereto, whereinat least part of the eccentric enlarged cutting head has a tissueremoving surface, which is typically an abrasive surface. In certainembodiments, the abrading head will be at least partially hollow. Whenplaced within an artery against stenotic tissue and rotated atsufficiently high speeds the eccentric nature of the enlarged cuttinghead causes the cutting head and drive shaft to rotate in such a fashionas to open the stenotic lesion to a diameter substantially larger thanthe outer diameter of the enlarged cutting head. Preferably theeccentric enlarged cutting head has a center of mass spaced radiallyfrom the rotational axis of the drive shaft, facilitating the ability ofthe device to open the stenotic lesion to a diameter substantiallylarger than the outer diameter of the enlarged cutting head whenoperated at high speeds.

The eccentric abrading head disclosed in application Ser. No. 11/761,128comprises proximal, distal and intermediate surfaces. The proximal anddistal surfaces are disclosed as each having a leading edge surface thatis substantially perpendicular to the drive shaft to which the device isattached. This raised edge surface may make it more difficult tonavigate difficult stenoses without damaging the vessel lining and couldbe improved upon. The disclosure of application Ser. No. 11/761,128 isincorporated herein in its entirety insofar as it discloses the featuresdiscussed above.

The present invention overcomes these deficiencies and provides theabove-referenced improvements.

BRIEF SUMMARY OF THE INVENTION

The invention provides a rotational atherectomy device having, invarious embodiments, a flexible, elongated, rotatable drive shaft withat least one flexible or inflexible eccentric enlarged abrading andcutting head attached thereto which comprises an abrasive surface. Whenplaced against stenotic tissue and rotated at high speed, the eccentricnature of the abrading and cutting head moves along an orbital path,opening the lesion to a diameter larger than the resting diameter of theenlarged abrading and cutting head. Preferably the abrading and cuttinghead has a center of mass spaced radially from the rotational axis ofthe drive shaft, facilitating the ability of the device to travel alongan orbital path. The abrading and cutting head comprises proximal and/ordistal radiused surfaces that facilitate cutting difficult stenosismaterial while minimizing trauma to the vessel.

An object of the invention is to provide a high-speed rotationalatherectomy device having at least one at least partially flexibleeccentric abrading and cutting head having at least one abrasive surfacefor abrading and proximal and/or distal radiused edges to facilitateentry into stenoses with minimal vessel trauma.

Another object of the invention is to provide a high-speed rotationalatherectomy device having at least one non-flexible eccentric abradingand cutting head having at least one abrasive surface for abrading andproximal and/or distal radiused edges to facilitate entry into stenoseswith minimal vessel trauma.

Another object of the invention is to provide a high-speed rotationalatherectomy device having at least one at least partially flexibleeccentric abrading and cutting head radiused edges to facilitate entryinto stenoses with minimal vessel trauma and having a resting diametersmaller than its high-speed rotational diameter.

Another object of the invention to provide a high-speed rotationalatherectomy device having at least one non-flexible eccentric abradingand cutting head radiused edges to facilitate entry into stenoses withminimal vessel trauma and having a resting diameter smaller than itshigh-speed rotational diameter.

Another object of the invention is to provide a high-speed rotationalatherectomy device having at least one partially flexible eccentricabrading and cutting head with proximal and/or distal radiused edges andthat is capable of opening pilot holes in stenoses that nearly orcompletely block the subject blood vessel with minimal vessel trauma.

Another object of the invention is to provide a high-speed rotationalatherectomy device having at least one non-flexible eccentric abradingand cutting head with proximal and/or distal radiused edges and that iscapable of opening pilot holes in stenoses that nearly or completelyblock the subject blood vessel with minimal vessel trauma.

Another object of the invention is to provide a high-speed rotationalatherectomy device having at least one flexible eccentric abrading andcutting head with proximal and/or distal radiused edges and that flexesduring insertion and placement, providing an improved ability tonavigate tortuous lumens with minimal trauma.

Another object of the invention is to provide a high-speed rotationalatherectomy device having at least one non-flexible abrading andeccentric cutting head with proximal and/or distal radiused edges andthat does not flex during placement or high-speed rotational operation.

An embodiment is a high-speed rotational atherectomy device for openinga stenosis in an artery, comprising: a guide wire having a maximumdiameter less than a diameter of the artery; a flexible elongated,rotatable drive shaft advanceable over the guide wire; and an abradinghead attached to the drive shaft and comprising proximal, intermediateand distal portions. The proximal portion comprises a proximal outersurface having diameters that increase distally. The intermediateportion comprises a cylindrical intermediate outer surface that includesat least one tissue removal section. The distal portion comprises adistal outer surface having diameters that decrease distally. Theabrading head defines a drive shaft lumen therethrough at leastpartially traversed by the drive shaft. The abrading head has a centerof mass laterally displaced from a center of the drive shaft lumen. Theabrading head is formed from a material having a density in the range of8-22 g/cm³.

Another embodiment is a high-speed rotational atherectomy device foropening a stenosis in an artery having a given diameter, comprising: aguide wire having a maximum diameter less than the diameter of theartery; a flexible elongated, rotatable drive shaft advanceable over theguide wire, the drive shaft having a rotational axis; and at least oneeccentric abrading head attached to the drive shaft, the abrading headcomprising proximal, intermediate and distal portions, wherein theproximal portion comprises a proximal outer surface, the intermediateportion comprises an intermediate outer surface and the distal portioncomprises a distal outer surface, the proximal outer surface havingdiameters that increase distally and a proximal radiused edge, thedistal outer surface having diameters that decrease distally, and theintermediate outer surface being cylindrical, wherein at least theintermediate outer surface comprise tissue removal sections and whereinthe abrading head defines a drive shaft lumen therethrough and a hollowchamber, the drive shaft at least partially traversing the drive shaftlumen. The abrading head is formed from a material having a density inthe range of 8-22 g/cm³.

The figures and the detailed description which follow more particularlyexemplify these and other embodiments of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, which are as follows.

FIG. 1 is a perspective view of one embodiment of a rotationalatherectomy device and system comprising one embodiment of thenon-flexible eccentric cutting head of the invention.

FIG. 2 is perspective, broken-away view of a prior art flexibleeccentric cutting head formed from the drive shaft.

FIG. 3 is a broken-away, longitudinal cross-sectional view of a priorart eccentric cutting head formed from the drive shaft.

FIG. 4 is a broken-away, longitudinal cross-sectional view illustratingthe flexibility of a prior art flexible eccentric enlarged cutting headformed from the drive shaft.

FIG. 5 is a longitudinal cross-sectional view of a prior art solid andinflexible eccentric abrasive burr attached to a drive shaft.

FIG. 6 is a broken-away longitudinal cross-sectional view of a prior artabrasive crown having sharp proximal and distal edges.

FIG. 7 is a perspective view of one embodiment of the present invention.

FIG. 8 is a side view of one embodiment of the present invention.

FIG. 9 is a bottom view of one embodiment of the present invention.

FIG. 10 is a broken away cross-sectional view of one embodiment of thepresent invention.

FIG. 11 is a broken-away, longitudinal cross-sectional view illustratingthe geometry of one embodiment of the present invention.

FIGS. 12A-12C are transverse cross-sectional views of one embodiment ofthe eccentric cutting head of the invention.

FIG. 13 is a longitudinal cross-sectional view showing one embodiment ofthe cutting head of the invention in an at-rest (non-rotating) positionafter a stenosis has been substantially opened by the device.

FIG. 14 is a transverse cross-sectional view illustrating threedifferent positions of the rapidly rotating eccentric enlarged cuttinghead of an eccentric rotational atherectomy device of the invention.

FIG. 15 is a schematic diagram illustrating the three differentpositions of the rapidly rotating eccentric enlarged cutting head of aneccentric rotational atherectomy device of the invention shown in FIG.14.

FIG. 16 is a broken away side view of one embodiment of the presentinvention with flexibility slots integrated therein.

FIG. 17 is a schematic side-view drawing of the geometry involved duringuse of the eccentric abrading head.

FIG. 18 is a schematic end-on drawing of the geometry of FIG. 17.

FIG. 19 is a schematic drawing of an eccentric abrading head.

DETAILED DESCRIPTION OF THE INVENTION

While the invention is amenable to various modifications and alternativeforms, specifics thereof are shown by way of example in the drawings anddescribed in detail herein. It should be understood, however, that theintention is not to limit the invention to the particular embodimentsdescribed. On the contrary, the intention is to cover all modifications,equivalents, and alternatives falling within the spirit and scope of theinvention.

FIG. 1 illustrates one embodiment of a rotational atherectomy deviceaccording to the disclosure of commonly assigned U.S. patent applicationSer. No. 11/761,128. The device includes a handle portion 10, anelongated, flexible drive shaft 20 having an eccentric enlarged abradinghead 28, and an elongated catheter 13 extending distally from the handleportion 10. The drive shaft 20 is constructed from helically coiled wireas is known in the art and the abrading head 28 is fixedly attachedthereto. Further to the various embodiments of the drive shaft that arecontemplated by the present invention, the drive shaft's helicallycoiled wire may comprise as few as three wires or as many as 15 wiresand may have a right hand or a left hand winding as will be known to theskilled artisan. The catheter 13 has a lumen in which most of the lengthof the drive shaft 20 is disposed, except for the enlarged abrading head28 and a short section distal to the enlarged abrading head 28. Thedrive shaft 20 also contains an inner lumen, permitting the drive shaft20 to be advanced and rotated over a guide wire 15. A fluid supply line17 may be provided for introducing a cooling and lubricating solution(typically saline or another biocompatible fluid) into the catheter 13.

The handle 10 desirably contains a turbine (or similar rotational drivemechanism) for rotating the drive shaft 20 at high speeds. The handle 10typically may be connected to a power source, such as compressed airdelivered through a tube 16. A pair of fiber optic cables 25,alternatively a single fiber optic cable may be used, may also beprovided for monitoring the speed of rotation of the turbine and driveshaft 20. Details regarding such handles and associated instrumentationare well known in the industry, and are described, e.g., in U.S. Pat.No. 5,314,407, issued to Auth. The handle 10 also desirably includes acontrol knob 11 for advancing and retracting the turbine and drive shaft20 with respect to the catheter 13 and the body of the handle.

FIGS. 2-4 illustrate details of a prior art device comprising aneccentric enlarged diameter abrading section 28A of a drive shaft 20A.The drive shaft 20A comprises one or more helically wound wires 18 whichdefine a guide wire lumen 19A and a hollow cavity 25A within theenlarged abrading section 28A. Except for the guide wire 15 traversingthe hollow cavity 25A, the hollow cavity 25A is substantially empty. Theeccentric enlarged diameter abrading section 28A includes, relative tothe location of the stenosis, proximal 30A, intermediate 35A and distal40A portions. Wire turns 31 of the proximal portion 30A of the eccentricenlarged diameter section 28A preferably have diameters thatprogressively increase distally at a generally constant rate, therebyforming generally the shape of a cone. Wire turns 41 of the distalportion 40A preferably have diameters that progressively decreasedistally at a generally constant rate, thereby forming generally theshape of a cone. Wire turns 36 of the intermediate portion 35A areprovided with gradually changing diameters to provide a generally convexouter surface which is shaped to provide a smooth transition between theproximal and distal conical portions of the enlarged eccentric diametersection 28A of the drive shaft 20A.

Continuing with the prior art device of FIGS. 2-4, at least part of theeccentric enlarged diameter abrading section of the drive shaft 28A(preferably the intermediate portion 35A) comprises an external surfacecapable of removing tissue. A tissue removing surface 37 comprising acoating of an abrasive material 24A to define a tissue removing segmentof the drive shaft 20A is shown attached directly to the wire turns ofthe drive shaft 20A by a suitable binder 26A.

FIG. 4 illustrates the flexibility of the prior art eccentric enlargeddiameter abrading section of the drive shaft 28A, shown with drive shaft20A advanced over guide wire 15. In the embodiment shown, adjacent wireturns of the intermediate portion 35A of the eccentric enlarged cuttinghead of the drive shaft are secured to one another by the bindingmaterial 26A securing the abrasive particles 24A to the wire turns 36.Proximal portion 30A and distal 40A portion of the eccentric enlargeddiameter section of the drive shaft comprise wire turns 31 and 41,respectively, are not secured to one another, thereby permitting suchportions of the drive shaft to flex, as shown in the drawing. Suchflexibility facilitates advancement of the device through relativelytortuous passageways and, in some embodiments, flexing of the eccentricenlarged diameter abrading section 28A during high-speed rotation.Alternatively, adjacent wire turns 36 of the intermediate portion 35A ofthe eccentric enlarged diameter abrading section 28A of the drive shaftmay be secured to one another, thereby limiting the flexibility ofabrading section 28A.

FIG. 5 illustrates another prior art rotational atherectomy device whichemploys a solid asymmetrical abrasive burr 28B attached to a flexibledrive shaft 20B, rotated over a guide wire 15 such as provided by U.S.Pat. No. 5,681,336 to Clement. The drive shaft 20B may be flexible,however the solid asymmetrical abrasive burr 28B is inflexible. Theeccentric tissue removing burr 28B has a coating of abrasive particles24B secured to a portion of its outer surface by a suitable bindingmaterial 26B. This construction has limited utility, however because, asClement explains at Col. 3, lines 53-55, the asymmetrical burr 28B mustbe rotated at “lower speeds than are used with high speed ablationdevices, to compensate for heat or imbalance.” That is, given both thesize and mass of the solid burr-type construction, it is infeasible torotate such a burr at the high speeds used during atherectomyprocedures, i.e., 20,000-200,000 rpm. Essentially, the center of massoffset from the rotational axis of the drive shaft in this prior artdevice would result in development of significant centrifugal force,exerting too much pressure on the wall of the artery and creating toomuch heat, unnecessary trauma and excessively large particles.

FIG. 6 illustrates further one embodiment of the eccentric enlargedabrading head 28C disclosed in commonly assigned U.S. patent applicationSer. No. 11/761,128. In this embodiment, the drive shaft 20 isillustrated as attaching to the abrading head 28C in two separatesections, with a gap therebetween and the eccentric abrading head 28attached to both drive shaft sections. Alternatively, the drive shaft 20may be of single piece construction. A proximal portion 30 and thedistal portion 40 are shown with substantially equivalent lengths withintermediate portion 35 interposed therebetween. Proximal leading edge30A and distal leading edge 40A are illustrated as substantiallyperpendicular with drive shaft 20, thus forming hard and sharp edges E.Such hard and sharp edges may result in trauma to the vessel liningduring high-speed rotation; a result that is highly undesirable.

Turning now to FIGS. 7-11, one embodiment of the non-flexible, eccentricenlarged abrading head 28 of the rotational atherectomy device of theinvention will be discussed. The abrading head 28 may comprise at leastone tissue removing surface 37 on the external surface(s) of theintermediate portion 35, the distal portion 40 and/or the proximalportion 30 to facilitate abrasion of the stenosis during high speedrotation. The tissue removing surface 37 may comprise a coating of anabrasive material 24 bound to the external surface(s) of theintermediate portion 35, the distal portion 40 and/or the proximalportion 30 of abrading head 28. The abrasive material may be anysuitable material, such as diamond powder, fused silica, titaniumnitride, tungsten carbide, aluminum oxide, boron carbide, or otherceramic materials. Preferably the abrasive material is comprised ofdiamond chips (or diamond dust particles) attached directly to thetissue removing surface(s) by a suitable binder. Such attachment may beachieved using well known techniques, such as conventionalelectroplating or fusion technologies (see, e.g., U.S. Pat. No.4,018,576). Alternately the external tissue removing surface maycomprise mechanically or chemically roughening the external surface(s)of the intermediate portion 35, the distal portion 40 and/or theproximal portion 30 to provide a suitable abrasive tissue removingsurface 37. In yet another variation, the external surface may be etchedor cut (e.g., with a laser) to provide small but effective abradingsurfaces. Other similar techniques may also be utilized to provide asuitable tissue removing surface 37.

As best illustrated in FIGS. 9 and 10, an at least partially enclosedlumen or slot 23 may be provided longitudinally through the enlargedabrading head 28 along the rotational axis 21 of the drive shaft 20 forsecuring the abrading head 28 to the drive shaft 20 in a manner wellknown to those skilled in the art. In various embodiments, a hollowedchamber 25 may be provided to lessen and manipulate the mass (and centerof mass location relative to the drive shaft rotational axis 21) of theabrading head 28 to facilitate atraumatic abrasion and improvepredictability of control of the orbital pathway of the abrading head 28during high speed, i.e., 20,000 to 200,000 rpm, operation. As thoseskilled in the art will recognize, the orbital amplitude will bepredictably manipulated based upon the positioning of the center of massin relation to the rotational axis of the drive shaft. Thus, a largerhollowed chamber 25 will work to move the center of mass closer to therotational axis 21 than will a smaller hollowed chamber 25 (or nohollowed chamber 25) and, at a given rotational speed, will create asmaller orbital amplitude and/or diameter for the abrading head 28during high-speed rotation.

Each of the FIGS. 7-11 illustrates the radiused proximal and distaledges PR, DR. The rounded nature of the proximal edges PR, DRfacilitates gradual entry into a stenosis while minimizing anycollateral trauma to the vessel lining. There are any number of radiipossible for the distal and/or proximal edges PR, DR as those skilled inthe art will readily recognize; the entire range of such radii arewithin the scope of the present invention. The embodiment illustrated inthe Figures comprises radiused edges that are of equivalent radius,however the proximal and/or distal edges PR, DR may comprise radii thatare not equivalent. Moreover, in alternate embodiments, the abradinghead may comprise a proximal radiused edge while the distal end surfaceis not radiused. Still more alternatively, the distal edge may beradiused while the proximal end surface is not.

In the illustrated embodiment, the abrading head 28 may be fixedlyattached to the drive shaft 20, wherein the drive shaft comprises onesingle unit. Alternatively, as will be discussed below, the drive shaft20 may comprise two separate pieces, wherein the enlarged eccentricabrading head 28 is fixedly attached to both drive shaft 20 pieces, witha gap therebetween. This two-piece drive shaft construction techniquemay, in combination with hollowed chamber 25, allow further manipulationof the placement of the center of mass of the abrading head 28. The sizeand shape of the hollowed chamber 25 may be modified to optimize theorbital rotational path of the abrading head 28 for particularlydesirable rotational speeds. Those skilled in the art will readilyrecognize the various possible configurations, each of which is withinthe scope of the present invention.

The embodiment of FIGS. 7-11 illustrates the proximal portion 30 anddistal portion 40 of symmetrical shape and length. Alternate embodimentsmay increase the length of either the proximal portion 30 or the distalportion 40, to create an asymmetrical longitudinal profile.

Specifically with reference to FIG. 11, the drive shaft 20 has arotational axis 21 which is coaxial with the guide wire 15, the guidewire 15 being disposed within the lumen 19 of the drive shaft 20. Thus,the proximal portion 30 of the eccentric enlarged abrading head 28 hasan outer surface which is substantially defined by the lateral surfaceof a frustum of a cone, the cone having an axis 32 which intersects therotational axis 21 of the drive shaft 20 at a relatively shallow angleβ. Similarly, the distal portion 40 of the enlarged abrading head 28 hasan outer surface which is substantially defined by the lateral surfaceof a frustum of a cone, the cone having an axis 42 which also intersectsthe rotational axis 21 of the drive shaft 20 at a relatively shallowangle β. The cone axis 32 of the proximal portion 30 and the cone axis42 of the distal portion 40 intersect each other and are coplanar withthe longitudinal rotational axis 21 of the drive shaft.

The opposing sides of the cones generally should be at an angle α ofbetween about 10° and about 30° with respect to each other; preferablythe angle α is between about 20° and about 24°, and most preferably theangle α is about 22°. Also, the cone axis 32 of the proximal portion 30and the cone axis 42 of the distal portion 40 normally intersect therotational axis 21 of the drive shaft 20 at an angle of between about20° and about 8°. Preferably the angle is between about 3° and about 6°.

Although in the preferred embodiment shown in the drawings the angles αof the distal and proximal portions of the enlarged abrading head 28 aregenerally equal, they need not be equal. The same is true for the anglesβ.

In an alternate embodiment, the intermediate portion 35 may comprise adiameter that gradually increases from the intersection with the distalportion 40 to the intersection of the proximal portion 30. In thisembodiment, angle α, as illustrated in FIG. 6, may be larger in theproximal portion 30 than the distal portion 40, or vice versa. Furtheralternate embodiments comprise the intermediate portion 35 having asurface that is convex, wherein the intermediate portion outer surfacemay be shaped to provide a smooth transition between the proximal anddistal outer surfaces of the proximal and distal portions.

Because the cone axes 32 and 42 intersect the rotational axis 21 of thedrive shaft 20 at an angle β the eccentric enlarged abrading head 28 hasa center of mass that is spaced radially away from the longitudinalrotational axis 21 of the drive shaft 20. As will be described ingreater detail below, offsetting the center of mass from the driveshaft's axis of rotation 21 provides the enlarged abrading head 28 withan eccentricity that permits it to open an artery to a diametersubstantially larger than the nominal diameter of the enlarged eccentricabrading head 28. Preferably, the opened diameter is at least twice aslarge as the nominal resting diameter of the enlarged eccentric abradinghead 28.

FIGS. 12A-12C depict the positions of the centers of mass 29 of threecross-sectional slices (shown as faces of transverse cross-sections) ofthe eccentric enlarged abrading head 28 shown in FIGS. 7-11, with theeccentric enlarged abrading head 28 fixedly attached to the drive shaft20, the drive shaft 20 advanced over guide wire 15, the guide wire 15within drive shaft lumen 19. The entire eccentric enlarged abrading head28 may be divided into many such thin slices, each slice having its owncenter of mass. FIG. 12B is taken at a position where the eccentricenlarged abrading head 28 has its maximum cross-sectional diameter(which, in this embodiment, is the maximum diameter of the intermediateportion 35 of the eccentric enlarged abrading head 28). FIGS. 12A and12C are cross-sections, respectively, of the distal 40 and proximal 30portions of the eccentric enlarged abrading head 28. In each of thesecross-sectional slices the center of mass 29 is spaced away from therotational axis 21 of the drive shaft 20, the rotational axis of thedrive shaft 20 coinciding with the center of the guide wire 15. Thecenter of mass 29 of each cross-sectional slice also generally coincideswith the geometric center of such cross-sectional slice. FIG. 12Billustrates the cross sectional slice of intermediate portion 35,comprising the largest cross-sectional diameter of abrading head 28,wherein both the center of mass 29 and the geometric center are locatedthe furthest (i.e., maximally spaced away) from the rotational axis 21of the drive shaft 20 compared with proximal 30 and distal 40 portions.

It should be understood that, as used herein, the word “eccentric” isdefined and used herein to refer to either a difference in locationbetween the geometric center of the enlarged abrading head 28 and therotational axis 21 of the drive shaft 20, or to a difference in locationbetween the center of mass 29 of the enlarged abrading head 28 and therotational axis 21 of the drive shaft 20. Either such difference, at theproper rotational speeds, will enable the eccentric enlarged abradinghead 28 to open a stenosis to a diameter substantially greater than thenominal diameter of the eccentric enlarged abrading head 28. Moreover,for an eccentric enlarged abrading head 28 having a shape that is not aregular geometric shape, the concept of “geometric center” can beapproximated by locating the mid-point of the longest chord which isdrawn through the rotational axis 21 of the drive shaft 28 and connectstwo points on a perimeter of a transverse cross-section taken at aposition where the perimeter of the eccentric enlarged abrading head 28has its maximum length.

The abrading head 28 of the rotational atherectomy device of theinvention may be constructed of stainless steel, tungsten or similarmaterial. The abrading head 28 may be a single piece unitaryconstruction or, alternatively, may be an assembly of two or moreabrading head components fitted and fixed together to achieve theobjects of the present invention.

Those skilled in the art will recognize that the embodiments illustratedherein, including may comprise at least one tissue removing surface 37as described above. This tissue removing surface 37 may be disposed onone or more of the intermediate portion 35, proximal portion 30 and/ordistal portion 40 of the eccentric abrading head 28. The proximal and/ordistal radiused edges PR, DR may also comprise a tissue removing surfacewith an abrasive material disposed thereon as described herein.

In certain situations, including the one presently under discussion, theabrading head 28 may be used to gradually and atraumatically create anopening using the increasing diameter of the distal portion 40 of theabrading head 28 to increase the diameter of the opening untilsufficient plaque has been removed to allow advancement of the abradinghead 28 through and across the stenosis and then retraction thereof. Theability to create pilot holes is enhanced by several features. Thecone-shaped proximal portion 30 allows gradual advancement andcontrolled abrading access of the tissue removing surface 37 to thestenosis, creating a pilot hole for the continued advancement of theabrading head 28. The rounded radiused proximal and/or distal edges PR,DR further facilitate creation of a pilot hole and may, as describedherein, comprise an abrasive material and surface thereon to helpgradually and atraumatically open a pilot hole. Further, theintersections of the cone-shaped proximal portion 30 (and distal portion40, not shown in the figure) with the cylinder-shaped intermediateportion 35 of the abrading head 28 may define edges with an ability tocut or abrade plaque as the device is gradually advanced, thusincreasing the diameter of the abraded stenosis. Moreover, as discussedabove, the surfaces of the proximal portion 30, as well as theintermediate 35 and distal portions 40 (not shown in the figure) of theabrading head 28 may be covered in whole or in part with the abrasivematerial of the tissue removing surface 37, thus facilitating plaqueabrasion and opening of the stenosis in a gradual and controlled mannerduring advancement and retraction through the stenosis. Ultimately,sufficient plaque will be removed to allow the entire abrading head 28to be advanced across the stenosis and retracted.

In addition, the non-flexible abrading head 28 may be sizedappropriately for the creation of pilot holes through a stenosis,essentially creating access for successively larger abrading head(s) 28of the present invention to follow so that the opening is openedgradually, or perhaps creates a pilot hole to allow subsequent access bycertain prior art devices such as that described in Shturman U.S. Pat.No. 6,494,890, i.e., the flexible eccentric enlarged section of thedrive shaft. Such an arrangement may comprise using two separate devicesor combining the two (or more) within one device. For example, it may beadvantageous to place a non-flexible eccentric abrading head 28 of thepresent invention distally along the drive shaft 20 in combination witha more proximally placed flexible eccentric enlarged abrading section ofthe drive shaft 20 as disclosed in Shturman '890. In this embodiment, apilot hole may be opened using the non-flexible abrading head 28, sothat the flexible eccentric enlarged abrading section of the drive shaft20 may follow through the stenosis, opening it still further.Alternatively, successively larger non-flexible abrading heads 28 may beplaced in series along the drive shaft 20, the smallest being mostdistal along the drive shaft 20, i.e., most proximal to the stenosis.Still more alternatively, a combination of non-flexible and flexible(discussed herein), eccentric abrading heads 28 may be provided inseries along the drive shaft 20.

FIG. 13 depicts the enlarged eccentric abrading head 28 of the presentinvention with guide wire 20 and the attached abrading head 28 advancedover guide wire 15 and in an “at-rest” position within the artery “A”,after the stenosis has been substantially opened, thus illustrating thedevice's ability to open a stenosis to a diameter well in excess of thedevice's nominal diameter.

The extent to which a stenosis in an artery can be opened to a diameterlarger than the nominal diameter of the eccentric enlarged abrading headof the present invention depends on several parameters, including theshape of the eccentric enlarged abrading head, the mass of the eccentricenlarged abrading head, the distribution of that mass and, therefore,the location of the center of mass within the abrading head with respectto the rotational axis of the drive shaft, and the speed of rotation.

The speed of rotation is a significant factor in determining thecentrifugal force with which the tissue removing surface of the enlargedabrading head is pressed against the stenotic tissue, thereby permittingthe operator to control the rate of tissue removal. Control of therotational speed also allows, to some extent, control over the maximumdiameter to which the device will open a stenosis. Applicants have alsofound that the ability to reliably control the force with which thetissue removing surface is pressed against the stenotic tissue not onlypermits the operator to better control the rate of tissue removal butalso provides better control of the size of the particles being removed.

FIGS. 14-15 illustrate the generally spiral orbital path taken byvarious embodiments of the eccentric abrading head 28 of the presentinvention, the abrading head 28 shown relative to the guide wire 15 overwhich the abrading head 28 has been advanced. The pitch of the spiralpath in FIG. 14-15 is exaggerated for illustrative purposes. In reality,each spiral path of the eccentric enlarged abrading head 28 removes onlya very thin layer of tissue via the tissue removing surface 37, andmany, many such spiral passes are made by the eccentric enlargedabrading head 28 as the device is repeatedly moved forward and backwardacross the stenosis to fully open the stenosis. FIG. 14 showsschematically three different rotational positions of the eccentricenlarged abrading head 28 of a rotational atherectomy device of theinvention. At each position the abrasive surface of the eccentricenlarged abrading head 28 contacts the plaque “P” to be removed—thethree positions are identified by three different points of contact withthe plaque “P”, those points being designated in the drawing as pointsB1, B2, and B3. Notice that at each point it is generally the sameportion of the abrasive surface of the eccentric enlarged abrading head28 that contacts the tissue. The portion of the tissue removing surface37 that is radially most distant from the rotational axis of the driveshaft.

In addition to the non-flexible abrading head embodiments describedabove, various embodiments of the present invention further comprisesome flexibility in the eccentric abrading head 28. Exemplaryembodiments are illustrated in FIGS. 15-18.

FIG. 15 illustrates an abrading head similar to that provided in FIGS.7-11 but with flexibility slots 46 being disposed on the abrading head28. The slots 46 are illustrated as being cut completely through theabrading head 28 and into lumen 23 to allow for maximum flex of theabrading head 28. However, the skilled artisan will recognize that theslots 46 need not extend into lumen 23 and may instead achieveflexibility by in effect scoring the abrading head 28 but not extendinginto lumen 23. In various embodiments, abrading head 28 will flex withthe flexible drive shaft 20 to ease negotiation of tortuous passagewayswithin the subject lumen. Such flexibility in the abrading head 28 thusmay provide a less traumatic entry enroute to the lesion to be abradedas well as a less traumatic exit therefrom. At least one flexibilityslot 46 is required to provide such flexibility; preferably a pluralityof flexibility slots 46 will be provided.

The embodiment of the flexible abrading head 28 of FIG. 15 illustrates aseries of evenly placed flexibility slots 46 of substantially consistentwidth and depth wherein the slots 46 are cut completely through theabrading head 28 to the lumen 23 therein. Those skilled in the art willrecognize that the flexibility of the abrading head 28 may becontrolled, i.e., modified, through manipulation of, among other things,one or more of the following elements: number of slots 46; depth ofslots 46 within abrading head 28; width of slots 46; angle of cut ofslots 46; placement of the slots 46 on the abrading head 28.

Thus, the flexibility characteristics of the abrading head may becontrolled or modified using flexibility slots 46. Certain embodimentsof the present invention may comprise, e.g., flexibility slots 46concentrated near the center of the abrading head 28, i.e., arrangedwithin the intermediate portion 35, with only one slot 46 engaging theproximal portion 30 and only one slot 46 engaging the distal portion 40.It will be obvious to the skilled artisan that many equivalents arepossible, each of which are within the scope of the present invention.

Each of the flexible abrading head embodiments may comprise abrasivematerial disposed thereon as discussed above in connection with thenon-flexible embodiments.

Thus the eccentric abrading head 28 of the present invention maycomprise non-flexible and/or at least partially flexible embodiments.

Although not wishing to be constrained to any particular theory ofoperation, applicants believe that offsetting the center of mass fromthe axis of rotation produces an “orbital” movement of the enlargedabrading head, the diameter of the “orbit” being controllable byvarying, among other things, the rotational speed of the drive shaft.Whether or not the “orbital” movement is as geometrically regular as isshown in FIGS. 14-15 has not been determined, but applicants haveempirically demonstrated that by varying the rotational speed of thedrive shaft one can control the centrifugal force urging the tissueremoving surface of the eccentric enlarged abrading head 28 against thesurface of the stenosis. The centrifugal force can be determinedaccording to the formula:

F _(c) =mΔx(πn/30)²

where F_(c) is the centrifugal force, m is the mass of the eccentricenlarged abrading head, Δx is the distance between the center of mass ofthe eccentric enlarged abrading head and the rotational axis of thedrive shaft, and n is the rotational speed in revolutions per minute(rpm). Controlling this force F_(c) provides control over the rapiditywith which tissue is removed, control over the maximum diameter to whichthe device will open a stenosis, and improved control over the particlesize of the tissue being removed.

The abrading head 28 of the present invention comprises more mass thanprior art high speed atherectomy abrading devices. As a result, a largerorbit may be achieved during high speed rotation which, in turn, allowsfor use of a smaller abrading head than with prior art devices. Inaddition to allowing for the creation of pilot holes in completely orsubstantially blocked arteries and the like, using a smaller abradinghead will allow for greater ease of access and less trauma duringinsertion.

Operationally, using the rotational atherectomy device of the inventionthe eccentric enlarged abrading head 28 is repeatedly moved distally andproximally through the stenosis. By changing the rotational speed of thedevice one can control the force with which the tissue removal surfaceis pressed against the stenotic tissue, thereby better controlling thespeed of the plaque removal as well as the particle size of tissueremoved. Since the stenosis is being opened to a diameter larger thanthe nominal diameter of the enlarged eccentric abrading head 28, thecooling solution and the blood are able to constantly flow around theenlarged abrading head. Such constant flow of blood and cooling solutionconstantly flushes away removed tissue particles, thus providing uniformrelease of removed particles, once the abrading head has passed throughthe lesion once.

The eccentric enlarged abrading head 28 may comprise a maximumcross-sectional diameter ranging between about 1.0 mm to about 3.0 mm.Thus, the eccentric enlarged abrading head may comprise cross-sectionaldiameters including, but not limited to: 1.0 mm, 1.25 mm, 1.50 mm, 1.75mm, 2.0 mm, 2.25 mm, 2.50 mm, 2.75 mm, and 3.0 mm. Those skilled in theart will readily recognize that the incremental increases of 0.25 mmwithin the above-listing of cross-sectional diameter are exemplary only,the present invention is not limited by the exemplary listing and, as aresult, other incremental increases in cross-sectional diameter arepossible and within the scope of the present invention.

Because, as described above, the eccentricity of the enlarged abradinghead 28 is dependent on a number of parameters, applicants have foundthat the following design parameters may be considered regarding thedistance between the rotational axis 21 of the drive shaft 20 and thegeometric center of a face of a transverse cross-section, taken at aposition of maximum cross-sectional diameter of the eccentric enlargedabrading head: for a device having an eccentric enlarged abrading headwith a maximum cross-sectional diameter between about 1.0 mm and about1.5 mm, desirably the geometric center should be spaced away from therotational axis of the drive shaft by a distance of at least about 0.02mm, and preferably by a distance of at least about 0.035 mm; for adevice having an eccentric enlarged abrading head with a maximumcross-sectional diameter between about 1.5 mm and about 1.75 mm,desirably the geometric center should be spaced away from the rotationalaxis of the drive shaft by a distance of at least about 0.05 mm,preferably by a distance of at least about 0.07 mm, and most preferablyby a distance of at least about 0.09 mm; for a device having aneccentric enlarged abrading head with a maximum cross-sectional diameterbetween about 1.75 mm and about 2.0 mm, desirably the geometric centershould be spaced away from the rotational axis of the drive shaft by adistance of at least about 0.1 mm, preferably by a distance of at leastabout 0.15 mm, and most preferably by a distance of at least about 0.2mm; and for a device having an eccentric enlarged abrading head with amaximum cross-sectional diameter above 2.0 mm, desirably the geometriccenter should be spaced away from the rotational axis of the drive shaftby a distance of at least about 0.15 mm, preferably by a distance of atleast about 0.25 mm, and most preferably by a distance of at least about0.3 mm.

Design parameters can also be based on the location of the center ofmass. For a device having an eccentric enlarged abrading head 28 with amaximum cross-sectional diameter between about 1.0 mm and about 1.5 mm,desirably the center of mass should be spaced away from the rotationalaxis of the drive shaft by a distance of at least about 0.013 mm, andpreferably by a distance of at least about 0.02 mm; for a device havingan eccentric enlarged abrading head 28 with a maximum cross-sectionaldiameter between about 1.5 mm and about 1.75 mm, desirably the center ofmass should be spaced away from the rotational axis of the drive shaftby a distance of at least about 0.03 mm, and preferably by a distance ofat least about 0.05 mm; for a device having an eccentric enlargedabrading head with a maximum cross-sectional diameter between about 1.75mm and about 2.0 mm, desirably the center of mass should be spaced awayfrom the rotational axis of the drive shaft by a distance of at leastabout 0.06 mm, and preferably by a distance of at least about 0.1 mm;and for a device having an eccentric enlarged abrading head with amaximum cross-sectional diameter above 2.0 mm, desirably the center ofmass should be spaced away from the rotational axis of the drive shaftby a distance of at least about 0.1 mm, and preferably by a distance ofat least about 0.16 mm.

Preferably, the thickness of the wall 50, e.g., as illustrated in FIG.10C, separating the hollow chamber from the outer surfaces defined bythe proximal 30, intermediate 35 and/or distal 40 portions should be aminimum of 0.2 mm thick to preserve stability and integrity of thestructure.

Preferably the design parameters are selected so that the enlargedabrading head 28 is sufficiently eccentric that, when rotated over astationary guide wire 15 (held sufficiently taut so as to preclude anysubstantial movement of the guide wire) at a rotational speed greaterthan about 20,000 rpm, at least a portion of its tissue removing surface37 may rotate through a path (whether or not such path is perfectlyregular or circular) having a diameter larger than the maximum nominaldiameter of the eccentric enlarged abrading head 28. For example, andwithout limitation, for an enlarged abrading head 28 having a maximumdiameter between about 1.5 mm and about 1.75 mm, at least a portion ofthe tissue removal surface 37 may rotate through a path having adiameter at least about 10% larger than the maximum nominal diameter ofthe eccentric enlarged abrading head 28, preferably at least about 15%larger than the maximum nominal diameter of the eccentric enlargedabrading head 28, and most preferably at least about 20% larger than themaximum nominal diameter of the eccentric enlarged abrading head 28. Foran enlarged abrading head having a maximum diameter between about 1.75mm and about 2.0 mm, at least a portion of the tissue removal sectionmay rotate through a path having a diameter at least about 20% largerthan the maximum nominal diameter of the eccentric enlarged abradinghead 28, preferably at least about 25% larger than the maximum nominaldiameter of the eccentric enlarged abrading head 28, and most preferablyat least about 30% larger than the maximum nominal diameter of theeccentric enlarged abrading head 28. For an enlarged abrading head 28having a maximum diameter of at least about 2.0 mm, at least a portionof the tissue removal surface 37 may rotate through a path having adiameter at least about 30% larger than the maximum nominal diameter ofthe eccentric enlarged abrading head 28, and preferably at least about40% larger than the maximum nominal diameter of the eccentric enlargedabrading head 28.

Preferably design parameters are selected so that the enlarged abradinghead 28 is sufficiently eccentric that, when rotated over a stationaryguide wire 15 at a speed between about 20,000 rpm and about 200,000 rpm,at least a portion of its tissue removing surface 37 rotates through apath (whether or not such path is perfectly regular or circular) with amaximum diameter that is substantially larger than the maximum nominaldiameter of the eccentric enlarged abrading head 28. In variousembodiments, the present invention is capable of defining asubstantially orbital path with a maximum diameter that is incrementallybetween at least about 50% and about 400% larger than the maximumnominal diameter of the eccentric enlarged abrading head 28. Desirablysuch orbital path comprises a maximum diameter that is between at leastabout 200% and about 400% larger than the maximum nominal diameter ofthe eccentric enlarged abrading head 28.

We turn to a more detailed analysis of the forces and displacementsassociated with the eccentric abrading head, particularly thoseassociated with the density of the material used to form the eccentricabrading head.

The actual orbital motion of the abrading head may be quite irregular,as described above. However, for the purposes of this analysis, it isassumed that the system is in equilibrium, with the drive shaft rotatingat angular velocity ω, and the eccentric abrading head rotating alongwith the drive shaft at a single distance away from the rotational axisof the drive shaft. In practice, such rotational stability may rarelyoccur, but for analysis of trends, it is adequate.

FIGS. 17 and 18 are schematic side-view and end-on drawings,respectively, of the geometry involved during use of the eccentricabrading head 28.

An eccentric abrading head 28 is attached to the drive shaft 20. Itscenter of mass, labeled “CM” in FIGS. 17 and 18, is deliberatelylaterally displaced away from the drive shaft 20 by an eccentricity,represented by a distance e.

The drive shaft 20 rotates at an angular velocity (or rotational speed)ω, which is typically in units radians/second, although it may also bein units of degrees/second or revolutions/second, revolutions/minute(rpm), or any other suitable unit of angle per time.

During use, the drive shaft 20 deflects laterally away from its nominalrotational axis 59 by a distance r. The deflection is directed radiallyoutward from the nominal axis 59. Such an outward deflection may bereferred to as centrifugal acceleration or acceleration due to acentrifugal force. Strictly speaking, centrifugal force is caused by theinertia of the drive shaft and eccentric abrading head 28, and is notexplicitly applied by any particular body that pushes radially outwardon the abrading head 28. Still, the term is useful and is used herein todenote the “apparent” force that pushes outward on a body as it rotates.

The drive shaft 20 (along with the guide wire, which typically remainswithin the drive shaft throughout the procedure) pulls the eccentricabrading head 28 radially inward toward the nominal rotational axis 59.This inward deflection may be referred to as centripetal acceleration oracceleration due to a centripetal force. Unlike the centrifugal force,the centripetal force originates with a real object, namely the driveshaft 20 (along with the guide wire). When the system is in equilibrium,the centrifugal and centripetal forces are equal and opposite; theiramplitudes are equal and their directions are opposite each other.

We may write the amplitude of the centrifugal force, F_(c), as:

F _(c) =mω ²(r+e),

where F_(c) is the force (typically in newtons, N, or kg-m/s², althoughunits of pound-force or pounds may be used), m is the mass of theeccentric abrading head (typically in kg, although units of slugs,pound-mass or pounds may be used), ω is the angular velocity (orrotational speed) of the drive shaft (typically in radians/s, althoughunits of degrees/s or revolutions/s, or revolutions/minute may be used),and r and e are distances as shown in FIGS. 17 and 18 (typically in m,although units of inches or mm may be used).

The restoring force, or centripetal force, is the force exerted by thestiffness of the drive shaft (along with the guide wire), which isdirected radially inward. We may treat the drive shaft (along with theguide wire) as a linear spring, which exerts a radial force that isdirectly proportional to its radial displacement away from its nominalposition. The ratio of radial force, divided by radial displacement, isknown as a “spring constant”, denoted by k. Spring constants k are inunits of force per length (typically in N/m, or kg/s², although units ofpounds/inch, pounds/m, or slug/s² may be used).

We may write the amplitude of the centripetal (restoring) force, F_(k),as:

F_(k)=kr.

We assume that the system is in equilibrium, as noted above, so that theamplitudes of the centrifugal and restoring forces are equal. We setF_(k) equal to F_(c) and solve for the distance r:

$r = {e\frac{\omega^{2}}{\frac{k}{m} - \omega^{2}}}$

Note that for the above equation, there is a critical angular velocityω, equal to (k/m)^(1/2), at which the radial deflection of the driveshaft r becomes infinite. In practice, one would certainly not see aninfinite radial deflection, but one might see large and potentiallydamaging resonances at angular velocities near the critical angularvelocity (k/m)^(1/2). In practice, such critical angular velocities arewell known, and devices are typically run well above or well below thecritical values.

Typically, each procedure uses one specific value of ω, such as 20,000rpm or any other suitable value. For analyzing dependencies or trends,we may consider the angular velocity ω to be constant.

We consider the effect of using different materials for the eccentricabrading head 28. Because a present abrading head 28 is made from asingle uniform material, the center of mass CM remains in the samelocation for all choices of material. Such a center of mass is afunction only of the volume distribution of the abrading head, and isunaffected by mass m or material density (mass per volume).

If we form the abrading head from a more dense material, m increases, eremains constant because the center of mass does not move, k remainsconstant because it is a function of the drive shaft (along with theguide wire), and ω remains constant for the particular procedure. Thedenominator of the above equation decreases, and the radial deflection rof the drive shaft increases.

In other words, the more dense the eccentric abrading head material (allother quantities being equal), the larger the outward radial deflectionof the drive shaft as it spins. This may be desirable in some cases, asit would allow for the cleaning of larger diameter blood vessels.

One can look at this a different way. Instead of changing material tomake the abrading diameter larger, as above, we can show that bychanging to a more dense material, we can use a smaller abrading head toachieve comparable performance (i.e., the same radial deflection of thedrive shaft).

We may return to the above equation and solve for the eccentricity e:

$e = {r\frac{\frac{k}{m} - \omega^{2}}{\omega^{2}}}$

Here, the radial deflection of the drive shaft, r, remains constant andequal to a desired value. For a more dense material, having a higherdensity, the mass m increases, so the numerator of the above equationdecreases. As a result, the required eccentricity e decreases. If therequired eccentricity decreases, the entire abrading head may be scaleddown to accommodate the decreased eccentricity.

Ultimately, a smaller abrading head may be beneficial for reasons thatapply prior to and after the procedure is performed. For instance, asmaller head may be used with a smaller-diameter catheter, which may beeasier to feed through the relevant blood vessels en route to theblockage.

It should be noted that the above numerical analysis used radialdeflection as a figure of merit to determine performance. Alternatively,other figures of merit may be used. For instance, one may use anabrading radius, shown as d in FIG. 18.

FIG. 19 shows three cross-sectional views of the abrasive head 28, alongwith its center of mass, labeled CM. Although it is possible to deriveclosed-form expressions that give the center of mass as a function ofthe head dimensions, such expressions are generally cumbersome, andprovide little more insight than the overly simplistic expressionsconsidered above.

As another example, one may also factor in the forces transmitted fromthe spinning abrading head to the material in the blockage itself. Suchrelationships may use fundamental physical quantities, such as velocity,force, and/or momentum (mass times velocity), and/or may use physicalquantities associated with a particular event, such as impulse (changein momentum for the event) and/or impact force (change in momentumdivided by an event length).

The mathematical relationships for the abrading diameter, or for otherphysical quantities, are more complicated than those presented above,but the general conclusions are the same: more dense materials may bepreferable for the abrading head.

Any or all of the following materials may be suitable for forming theeccentric abrading head, including Grade 304 Stainless Steel (sometimesreferred to as standard “18/8” stainless) (with a density of 8.0 g/cm³),Grade 303 Stainless Steel (also 8.0 g/cm³), MP35N (an alloy ofnickel-cobalt-chromium-molybdenum) (8.4 g/cm³), L605 (an alloy ofchromium-nickel-tungsten-cobalt) (9.1 g/cm³), and the following metals,used alone, in combination or in an alloy form: niobium (8.4 g/cm³),cobalt (8.9 g/cm³), nickel (8.9 g/cm³), molybdenum (10.2 g/cm³), silver(10.5 g/cm³), palladium (12.0 g/cm³), tantalum (16.6 g/cm³), tungsten(19.3 g/cm³), gold (19.3 g/cm³), rhenium (21.0 g/cm³), platinum (21.4g/cm³), and iridium (22.5 g/cm³).

One may specify the materials in terms of their respective densities,which may be grouped into ranges, such as 7-22 g/cm³, 8-22 g/cm³, 10-22g/cm³, 11-22 g/cm³, 15-22 g/cm³, 18-22 g/cm³, 20-22 g/cm³, 22-22 g/cm³,7-22 g/cm³, 8-22 g/cm³, 10-22 g/cm³, 11-22 g/cm³, 15-22 g/cm³, 18-22g/cm³, 20-22 g/cm³, 22-22 g/cm³, 7-22 g/cm³, 8-22 g/cm³, 10-22 g/cm³,11-22 g/cm³, 15-22 g/cm³, 18-22 g/cm³, 20-22 g/cm³, 7-20 g/cm³, 8-20g/cm³, 10-20 g/cm³, 11-20 g/cm³, 15-20 g/cm³, and/or 18-20 g/cm³.

The present invention should not be considered limited to the particularexamples described above, but rather should be understood to cover allaspects of the invention. Various modifications, equivalent processes,as well as numerous homogeneous or heterogeneous macro and microstructures to which the present invention may be applicable will bereadily apparent to those of skill in the art to which the presentinvention is directed upon review of the present specification.

1. A high-speed rotational atherectomy device for opening a stenosis inan artery, comprising: a guide wire having a maximum diameter less thana diameter of the artery; a flexible elongated, rotatable drive shaftadvanceable over the guide wire; and an abrading head attached to thedrive shaft and comprising proximal, intermediate and distal portions;wherein the proximal portion comprises a proximal outer surface havingdiameters that increase distally; wherein the intermediate portioncomprises a cylindrical intermediate outer surface that includes atleast one tissue removal section; wherein the distal portion comprises adistal outer surface having diameters that decrease distally; whereinthe abrading head defines a drive shaft lumen therethrough at leastpartially traversed by the drive shaft; wherein the abrading head has acenter of mass laterally displaced from a center of the drive shaftlumen; and wherein the abrading head is formed from a material having adensity in the range of 8-22 g/cm³.
 2. The device of claim 1, whereinthe abrading head is formed from a material having a density in therange of 8-22 g/cm³.
 3. The device of claim 2, wherein the abrading headis formed from tantalum, having a density of 16.6 g/cm³.
 4. The deviceof claim 2, wherein the abrading head is formed from an alloy oftantalum.
 5. The device of claim 2, wherein the abrading head is formedfrom tungsten, having a density of 19.3 g/cm³.
 6. The device of claim 2,wherein the abrading head is formed from an alloy of tungsten.
 7. Thedevice of claim 1, wherein the abrading head is formed from molybdenum,having a density of 10.2 g/cm³.
 8. The device of claim 1, wherein theabrading head is formed from an alloy of molybdenum.
 9. The device ofclaim 1, wherein the abrading head is formed from iridium, having adensity of 22.5 g/cm³.
 10. The device of claim 1, wherein the abradinghead is formed from an alloy of iridium.
 11. A high-speed rotationalatherectomy device for opening a stenosis in an artery having a givendiameter, comprising: a guide wire having a maximum diameter less thanthe diameter of the artery; a flexible elongated, rotatable drive shaftadvanceable over the guide wire, the drive shaft having a rotationalaxis; and at least one eccentric abrading head attached to the driveshaft, the abrading head comprising proximal, intermediate and distalportions, wherein the proximal portion comprises a proximal outersurface, the intermediate portion comprises an intermediate outersurface and the distal portion comprises a distal outer surface, theproximal outer surface having diameters that increase distally and aproximal radiused edge, the distal outer surface having diameters thatdecrease distally, and the intermediate outer surface being cylindrical,wherein at least the intermediate outer surface comprise tissue removalsections and wherein the abrading head defines a drive shaft lumentherethrough and a hollow chamber, the drive shaft at least partiallytraversing the drive shaft lumen; and wherein the abrading head isformed from a material having a density in the range of 8-22 g/cm³. 12.The device of claim 11, wherein the abrading head is formed from amaterial having a density in the range of 8-22 g/cm³.
 13. The device ofclaim 12, wherein the abrading head is formed from tantalum, having adensity of 16.6 g/cm³.
 14. The device of claim 12, wherein the abradinghead is formed from an alloy of tantalum.
 15. The device of claim 12,wherein the abrading head is formed from tungsten, having a density of19.3 g/cm³.
 16. The device of claim 12, wherein the abrading head isformed from an alloy of tungsten.
 17. The device of claim 11, whereinthe abrading head is formed from molybdenum, having a density of 10.2g/cm³.
 18. The device of claim 11, wherein the abrading head is formedfrom an alloy of molybdenum.
 19. The device of claim 11, wherein theabrading head is formed from iridium, having a density of 22.5 g/cm³.20. The device of claim 11, wherein the abrading head is formed from analloy of iridium.